1. 4STAR Instrument Technology Development Dunagan, 1/13 4STAR: Spectrometer for Sky-Scanning, Sun- Tracking Atmospheric Research Instrument Design, Development and Field Testing A collaboration involving: NASA Ames: S. Dunagan, R. Johnson, J. Zavaleta, R. Walker, C. Chang, P. Russell, J. Redemann, J. Livingston PNNL: C. Flynn, B. Schmid

2. 4STAR Instrument Technology Development Dunagan, 2/13 OVERVIEW Scientific objectives for airborne sun-sky photometry Airborne sunphotometer heritage at Ames Research Center New technologies for 4STAR Other design considerations Instrument specification Ground and flight prototypes Ground and flight testing

3. 4STAR Instrument Technology Development Dunagan, 3/13 AIRBORNE SUNPOHOTOMETRY

4. 4STAR Instrument Technology Development Dunagan, 4/13 ANTICIPATED 4STAR DATA PRODUCTS Solar Direct Beam Atmospheric Transmittance Aerosol Optical Depth and Ångstrom exponent Aerosol Extinction (via aircraft vertical profiling) Gases: H 2 O, O 3, NO 2, (column and in profile) Angularly-resolved sky radiance inversions Scattering phase function, asymmetry parameter Aerosol size distributions, fine/coarse mode fraction Aerosol sphericity Aerosol absorption Zenith radiance cloud retrievals Cloud Optical Depth, Droplet effective Radius (with auxilliary measurements, Barker et al.) Cloudy/clear transition zone (Marshak, Chiu) Water vapor, liquid water, ice water fractionation (Daniels et al.)

5. 4STAR Instrument Technology Development Dunagan, 5/13 AIRBORNE SUNPHOTOMETER HISTORY AT ARC 4STAR(2012- AATS-6(1985-2001) AATS-14(1996-

6. 4STAR Instrument Technology Development Dunagan, 6/13 NEW TECHNOLOGIES Miniaturized direct beam collector with aperture-limited field of view New skylight collector with optical power for signal amplification Fiber Optics wave guides permit detectors to be separated from the pointing system Fiber optic rotary joint conveys optical signal across azimuth axis rotating interface COTS Stepping motor/resolver rotary actuators replace custom DC servomotors for motion control COTS diffraction grating spectrometers replace interference filters for spectral discrimination CCD (quantum) detectors replace photodiodes

7. 4STAR Instrument Technology Development Dunagan, 7/13 OTHER DESIGN CONSIDERATIONS Minimal intrusion into airsteam and symmetrical aero shape, to minimize variability in airloads and reduce impact to aircraft handling qualities Emergency landing conditions to withstand 16 G accelerations (forward); Aero gust loads to withstand 7 G (vertical) Sky scan data acquisition cycle to be completed in less than 100 seconds (1 km translation at 10 m/sec) Pressurized cabin for altitudes to 41000 ft MSL Water tight seal for external surface of windows; Easy access to optics for cleaning

8. 4STAR Instrument Technology Development Dunagan, 8/13 INSTRUMENT SPECIFICATIONS

9. 4STAR Instrument Technology Development Dunagan, 9/13 GROUND PROTOTYPES Proof of concept for fiber optic light collector and waveguide stability performance Test pointing accuracy and control authority for stepping motor actuators Migration to more flight like geometry, including miniaturized collection optics and coiled “clockspring” spiral wound fiber optic flexure for elevation axis Test of radiometric performance of Fiber Optic Rotary Joint (FORJ) Pitch, roll and yaw motion simulator to evaluate tracking system authority and performance

10. 4STAR Instrument Technology Development Dunagan, 10/13 FLIGHT INSTRUMENT

11. 4STAR Instrument Technology Development Dunagan, 11/13 PERFORMANCE TESTING Uniformity of the solar disk measurement across the filed of view Rejection of direct solar radiation by skylight collector optics Skylight Scan Comparison with Cimel (Aeronet)

12. 4STAR Instrument Technology Development Dunagan, 12/13 CURRENT TECHNOLOGY CAPABILITY Sun tracking across pressure differential. Yes, some issues with glint Entrance window contamination. Not yet Fiber optic couplings with <1% calibration stability (Connections/Rotation). Yes Irradiance calibration to 1% over a period of months. Not yet Radiance calibration to a few percent. Yes Stray light rejection: measure skylight down to within 3° of sun. Yes Sky scan within 100 seconds (10 km in flight). Yes Stray light inside spectrometers. Yes Key Technology Hurdles

13. 4STAR Instrument Technology Development Dunagan, 13/13 FUTURE WORK Extensive ground testing with tilt/yaw table to improve performance Radiometrically stable sun tracking through maneuvers Skylight collection efficiency and stray light rejection Series of 3 additional flight tests in preparation for scientific field campaign use DOE G1 aircraft Evaluate environmental factors Added Capability Sun tracking whole sky camera Window heaters Field radiance calibration